Read additional files from QGIS project file

[fgravin]

This is a proposal to slightly improve the developer experience while using the qgis-js API.

At the moment, we have to list all the files that are used within the QGIS project, beside the QGIS project file itself.
eg.

const source =
  "/Glacier_3857";
const files = ["glaciers.qgs","glaciers.gpkg", "glaciers_attachments.zip"];

It would be great if the additional files could be guessed by the API by reading the QGIS project file.

[boardend]

Agree, it would be nice to just point to a project and query all involved files from there

Would be easy to expose/implement, if QGIS provides something like this internally, cc @wonder-sk.

Note that there is also the @qgis-js/utils package that helps to download many files from a web server, a GitHub repo, or the local file system